Ventilation dampers are devices that are used, by way of example, to control the flow of air into ventilation ducts, rooms, or other spaces of a building or facility. For example, a ventilation damper may help control the flow of cool air in to a room. In another example, a ventilation damper may control the amount of exhaust air from a building that is recirculated into the fresh air. Ventilation dampers are movable such that they may be further opened or closed in order to increase or decrease, respectively, the flow of air through the damper assembly device. In building control systems, damper assembly devices are also known as variable-air-volume (VAV) diffusers or VAV units.
One example of a VAV unit and its operation is set forth in U.S. Pat. No. 6,581,847, which is incorporated herein by reference. The VAV unit of U.S. Pat. No. 6,581,847 teaches the control of room temperature using a VAV unit to vary the volume of supply air discharged into a room. The supply air is heated when the VAV unit is in a heating mode and is cooled when the system is in cooling mode. The supply air is usually provided at substantially a constant temperature in each mode. A VAV unit regulates the volume of heated or cooled supply air in order to achieve and maintain a desired room air temperature. To this end, a controlled actuator device operates to open or close a set of louvers or ventilation dampers to increase or decrease to flow of supplied air.
Typical controlled actuator devices include thermally-powered actuators, pneumatically-powered actuators, and electrically powered actuators. All three types of actuators are coupled to the ventilation dampers by a mechanical linkage, gear assembly levers and/or combinations of these and other mechanical couplings. The actuator performs controlled movements which are translated by the mechanical couplings to changes in the positions of the dampers.
Control units for VAV units preferably maintain accurate information regarding the current position of the dampers. Accurate position information is useful for various reasons, including effective control and reliability. Inaccurate position information can even result in damage to a VAV unit. In one example, if a damper is fully open, and the position information indicates that the damper is not fully open, then the control mechanism may attempt to further open the damper. The attempt to further open the damper that is fully open is both inefficient and potentially harmful to the equipment.
Current VAV units employ various methods to maintain position information of dampers. One method is to derive the damper position from position information relating to the actuator device or the mechanical coupling. For example, in a VAV unit that includes drive gears that move mechanical linkages attached to the damper, the rotational position of the drive gear may be correlated to the position of the damper blades themselves.
The types of damper position measurements that are currently used cannot always reliably produce the level of accuracy that is necessary for high quality performance of control systems. To address this issue, those in the field have employed calibration techniques to improve the accuracy of various position methods. However, calibration techniques only provide limited improvement. Moreover, some degradation of accuracy can occur over time due to the nature of mechanical linkages, thereby reducing the effectiveness of the initial calibration.
Other methods include the use of limit switches on the damper blade itself. However, limit switches can provide little information regarding the position of the blades.
Accordingly, there is a need for improved accuracy in position measurements for use in damper or louver arrangements.